by Jennifer Collins and Gilgamesh Nabeel, Special for USA TODAY

by Jennifer Collins and Gilgamesh Nabeel, Special for USA TODAY

ISTANBUL - Ancient statues whispering of civilizations lost. Religious shrines from the Christian, Jewish and Islamic faiths. Tombs with relics and bones testifying to this region as the Cradle of Civilization - and where, in the city-states of Mesopotamia millennia ago, the world's first written language was born.

The land between the Tigris and Euphrates rivers has an estimated half-a-million archaeological sites and countless priceless artifacts. Only recently recovered and restored following the 2003 war in Iraq, they are nonetheless in danger once again, this time from Islamic extremists taking over large swaths of Iraq who deem this rich heritage "un-Islamic."

As Sunni Muslim insurgents loyal to the Islamic State in Iraq and the Levant - known as ISIL or ISIS - take cities such as Mosul and Tikrit, and advance toward Baghdad, they have in a published manifesto called on followers to destroy all "infidel" statues, churches, tombs and shrines.

Reports of church burnings and the destruction of shrines have already emerged from multicultural and ethnically diverse Mosul, which is being held by the insurgents. The city in Nineveh province has Assyrian Christian, Islamic and Jewish heritage and is the site of ancient churches and monasteries dating back to the 13th century.

Already in Mosul, ISIL has reportedly destroyed a shrine to the 11th century Kurdish historian Ali ibn al-Athir. There are fears that the same fate could befall important sites of early Christianity such as the "green church" in Tikrit. UNESCO world heritage sites, such as the ancient Arab city of Hatra that hosts temples from the first century blending Hellenistic and Roman architecture, may also be threatened.

"There has been no money for guarding sites and continuing programs of excavation and conservation," says Stephanie Dalley, an expert in ancient Iraq and a retired research fellow at the University of Oxford.

Archaeologists say other endangered sites include Khorsabad (ancient Dur Sharrukin), as well as Sufi and Shiite shrines and the monasteries and mosques of Tikrit.

Iraqis fear their rich historical legacy could be lost forever.

"Our heritage is in danger," says Hayder Reda, a lecturer at the applied medical sciences department at the University of Karbala, who is currently in Baghdad. "Terrorists will sell artifacts to fund themselves as they did in Afghanistan."

Islamic extremists have a history of destroying art, architecture and cultural sites deemed "un-Islamic."

In Afghanistan in 2001, the Taliban dynamited two towering Buddha statues carved into a cliff in the country's Bamiyan Valley, to international outcry. Built in the 6th century, the statues were a testament to the country's rich religious history. In 2012, Mali Islamists razed shrines seen as idolatrous in Timbuktu, some of which held the remains of revered Muslim scholars and teachers.

Iraq is home to three UNESCO world heritage sites and has centuries of pre-Islamic heritage. The ancient peoples of Sumer invented cuneiform, one of the earliest forms of writing, in the 4th millennium BC. They established sophisticated temple complexes, economies and irrigation. The region hosted numerous other ancient empires. Alexander the Great set up shop in Babylon, reputedly the home of the Hanging Gardens of Babylon, one of the seven ancient wonders of the world.

"Radical terrorism in the form of (the) Taliban, ISIL or al-Qaeda, is a real danger," says Salam Taha, a Jordan-based Iraqi engineer and archaeology enthusiast. "We all remember what happened to the Buddha statues of Bamiyan - despite all the international efforts, they insisted on committing their crime against our human heritage, (heritage) that belongs to people of all religions and ethnicities."

UNESCO on Tuesday called on Iraqis to protect the country's cultural heritage. "Their (the militants') intentional destruction (amount to) war crimes and (are) a blow against the Iraqi people's identity and history," says UNESCO Director-General Irina Bokova. But local archaeologists say the international community, including UNESCO, needs to act now to save the country's cultural treasures.

"This is an urgent call for the whole of humanity to save these precious archaeological sites," says Amer Abdul Razzaq, an Iraqi archaeologist from Nasiriyah, a city southeast of Baghdad. "The terrorists' (manifesto) seems serious and they will demolish the shrines and archaeological sites. I hope UNESCO will do something to guard and watch these sites."

Iraqis in some cities are trying to protect historical and religious sites and artifacts, just as staff at Kabul's National Museum saved priceless treasures from plunder and destruction by hiding them from foreign armed forces and the Taliban for 14 years until 2003.

"I am so worried," says Milad Kattan, a dentist currently in Erbil. "The archaeological sites are abandoned and nobody is taking care of them anywhere (in Iraq) even in Kurdistan. It is heartbreaking - after they have destroyed our present and future, they want to destroy our past, too."